U.S. patent application number 11/970239 was filed with the patent office on 2008-12-25 for signaling of random access preamble parameters in wireless networks.
Invention is credited to Pierre Bertrand, Jing Jiang.
Application Number | 20080316961 11/970239 |
Document ID | / |
Family ID | 40136387 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080316961 |
Kind Code |
A1 |
Bertrand; Pierre ; et
al. |
December 25, 2008 |
Signaling of Random Access Preamble Parameters in Wireless
Networks
Abstract
User equipment (UE)-initiated accesses within a cellular network
are optimized to account for cell size and to reduce signaling
overhead. A fixed set of preamble parameter configurations for use
across a complete range of cell sizes within the cellular network
is established and stored within each UE. A UE located in a given
cell receives a configuration number transmitted from a nodeB
serving the cell, the configuration number being indicative of a
size of the cell. The UE selects a preamble parameter configuration
from the fixed set of preamble parameter configurations in response
to the received configuration number and then transmits a preamble
from the UE to the nodeB using the preamble parameter configuration
indicated by the configuration number.
Inventors: |
Bertrand; Pierre; (Antibes,
FR) ; Jiang; Jing; (Allen, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Family ID: |
40136387 |
Appl. No.: |
11/970239 |
Filed: |
January 7, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60944913 |
Jun 19, 2007 |
|
|
|
61017542 |
Dec 29, 2007 |
|
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 24/02 20130101;
H04W 74/04 20130101; H04L 1/1812 20130101; H04L 5/0055 20130101;
H04W 74/004 20130101; H04W 74/0833 20130101; H04L 5/0051 20130101;
H04W 88/08 20130101; H04W 88/02 20130101; H04W 84/12 20130101; H04L
5/00 20130101; H04L 5/0032 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04Q 7/20 20060101
H04Q007/20 |
Claims
1. A method for transmitting from user equipment (UE) to base
stations (nodeB) in a cellular network, comprising: establishing a
fixed set of preamble parameter configurations for use across a
complete range of cell sizes within the cellular network; receiving
at a UE located in a cell a configuration number transmitted from a
nodeB serving the cell, the configuration number indicative of a
size of the cell; selecting a preamble parameter configuration
specified by the received configuration number from the fixed set
of preamble parameter configurations; and transmitting a preamble
from the UE to the nodeB using the preamble parameter configuration
indicated by the configuration number.
2. The method of claim 1, wherein each preamble parameter
configuration of the set of preamble parameter configurations
implicitly defines a number of root sequences and a number of
cyclic shifts per root sequence.
3. The method of claim 2, wherein the fixed set of preamble
parameter configurations comprises no more than sixteen preamble
parameter configurations and wherein the configuration number is
received using no more than four signaling bits.
4. The method of claim 2, wherein transmitting a preamble
comprises: determining the number of root sequences and the number
of cyclic shifts of the selected preamble parameter configuration;
mapping a predetermined number of preamble signatures to subsequent
cyclic shifts of a given root sequence according to the number of
cyclic shifts until the given root sequence is full, for all of the
number of root sequences until a last root sequence; adjusting the
number of cyclic shifts mapped onto the last root sequence such
that the predetermined number of preamble signatures are mapped;
and selecting one of the mapped preamble signatures for use in
transmitting the preamble.
5. The method of claim 4, wherein the predetermined number of
preamble signatures is sixty-four.
6. The method of claim 1, wherein the fixed set of preamble
parameter configurations sample the continuous cell size range
covered by the network in a non-linear way, such that a finer
configuration granularity is provided for smaller cells, whereby a
broader deployment of smaller cells compared to larger cells is
better supported.
7. A user equipment (UE) for use in a cellular network, comprising:
means for storing a fixed set of preamble parameter configurations
for use across a complete range of cell sizes within the cellular
network; means for receiving information by the UE within a given
cell that designates a particular preamble parameter configuration
from the fixed set of preamble parameter configurations; means for
selecting a preamble parameter configuration specified by the
received configuration number from the fixed set of preamble
parameter configurations; and means for transmitting a preamble
from the UE to the nodeB using the preamble parameter configuration
indicated by the configuration number.
8. The UE of claim 7, wherein each preamble parameter configuration
of the set of preamble parameter configurations implicitly defines
a number of root sequences and a number of cyclic shifts per root
sequence.
9. The UE of claim 8, wherein the fixed set of preamble parameter
configurations comprises no more than sixteen preamble parameter
configurations and wherein the configuration number is received
using no more than four signaling bits.
10. The UE of claim 8, wherein the means for transmitting a
preamble comprises: means for determining the number of root
sequences and the number of cyclic shifts of the selected preamble
parameter configuration; means for mapping a predetermined number
of preamble signatures to subsequent cyclic shifts of a given root
sequence according to the number of cyclic shifts until the given
root sequence is full, for all of the number of root sequences
until a last root sequence; means for adjusting the number of
cyclic shifts mapped onto the last root sequence such that the
predetermined number of preamble signatures are mapped; and means
for selecting one of the mapped preamble signatures for use in
transmitting the preamble.
11. A cellular telephone for use in a cellular network, comprising:
a receiver connected to an antenna operable to receive information
within a given cell that designates a particular configuration
number of a fixed set of preamble parameter configurations for use
across a complete range of cell sizes within the cellular network;
a processor connected to a storage memory holding instructions for
execution by the processor and for holding the fixed set of
preamble parameter configurations and connected to obtain signals
from the receiver, wherein the processor is operable to select a
preamble parameter configuration specified by the received
configuration number from the fixed set of preamble parameter
configurations; and a transmitter connected to the processor
operable to transmit a signal from the cellular telephone to the
NodeB using the selected preamble parameter configuration.
12. The cellular telephone of claim 1 1, wherein each preamble
parameter configuration of the set of preamble parameter
configurations implicitly defines a number of root sequences and a
number of cyclic shifts per root sequence.
13. The cellular telephone of claim 12, wherein the fixed set of
preamble parameter configurations comprises no more than sixteen
preamble parameter configurations and wherein the configuration
number is received using no more than four signaling bits.
14. The cellular telephone of claim 12, wherein the transmitter
comprises: circuitry for determining the number of root sequences
and the number of cyclic shifts of the selected preamble parameter
configuration; circuitry for mapping a predetermined number of
preamble signatures to subsequent cyclic shifts of a given root
sequence according to the number of cyclic shifts until the given
root sequence is full, for all of the number of root sequences
until a last root sequence; circuitry for adjusting the number of
cyclic shifts mapped onto the last root sequence such that the
predetermined number of preamble signatures are mapped; and
circuitry for selecting one of the mapped preamble signatures for
use in transmitting the preamble.
15. A method for transmitting from user equipment (UE) to base
stations (nodeB) in a cellular network, comprising: establishing a
fixed set of preamble parameter configurations for use across a
complete range of cell sizes within the cellular network;
determining a size of a cell being served by a nodeB; transmitting
to all UE located in the cell a configuration number from the nodeB
serving the cell, the configuration number indicative of the size
of the cell; and receiving a preamble transmitted from a UE located
with the cell using a preamble parameter configuration selected
from the fixed set of preamble parameter configurations specified
by the configuration number.
16. The method of claim 15, wherein each preamble parameter
configuration of the set of preamble parameter configurations
implicitly defines a number of root sequences and a number of
cyclic shifts per root sequence.
17. The method of claim 16, wherein the fixed set of preamble
parameter configurations comprises no more than sixteen preamble
parameter configurations and wherein the configuration number is
transmitted using no more than four signaling bits.
18. The method of claim 15, wherein the fixed set of preamble
parameter configurations sample the continuous cell size range
covered by the network in a non-linear way, such that a finer
configuration granularity is provided for smaller cells, whereby a
broader deployment of smaller cells compared to larger cells is
better supported.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to and incorporates
by reference U.S. provisional application No. 60/944,913 (attorney
docket TI-64591) filed on Jun. 19, 2007, entitled "Optimization of
Random Access Preamble Parameters Signaling in Wireless Networks."
The present application also claims priority to and incorporates by
reference U.S. provisional application No. 61/017,542 (attorney
docket TI-64410P) filed on Dec. 29, 2007, entitled "Signaling of
Random Access Preamble Parameters in Wireless Network."
FIELD OF THE INVENTION
[0002] This invention generally relates to wireless cellular
communication, and in particular to a non-synchronous request
channel for use in orthogonal and single carrier frequency division
multiple access (OFDMA) (SC-FDMA) systems.
BACKGROUND OF THE INVENTION
[0003] The Global System for Mobile Communications (GSM: originally
from Groupe Special Mobile) is currently the most popular standard
for mobile phones in the world and is referred to as a 2G (second
generation) system. Universal Mobile Telecommunications System
(UMTS) is one of the third-generation (3G) mobile phone
technologies. Currently, the most common form uses W-CDMA (Wideband
Code Division Multiple Access) as the underlying air interface.
W-CDMA is the higher speed transmission protocol designed as a
replacement for the aging 2G GSM networks deployed worldwide. More
technically, W-CDMA is a wideband spread-spectrum mobile air
interface that utilizes the direct sequence Code Division Multiple
Access signaling method (or CDMA) to achieve higher speeds and
support more users compared to the older TDMA (Time Division
Multiple Access) signaling method of GSM networks.
[0004] Orthogonal Frequency Division Multiple Access (OFDMA) is a
multi-user version of the popular Orthogonal Frequency-Division
Multiplexing (OFDM) digital modulation scheme. Multiple access is
achieved in OFDMA by assigning subsets of sub-carriers to
individual users. This allows simultaneous low data rate
transmission from several users. Based on feedback information
about the channel conditions, adaptive user-to-sub-carrier
assignment can be achieved. If the assignment is done sufficiently
fast, this further improves the OFDM robustness to fast fading and
narrow-band co-channel interference, and makes it possible to
achieve even better system spectral efficiency. Different number of
sub-carriers can be assigned to different users, in view to support
differentiated Quality of Service (QoS), i.e. to control the data
rate and error probability individually for each user. OFDMA is
used in the mobility mode of IEEE 802.16 WirelessMAN Air Interface
standard, commonly referred to as WiMAX. OFDMA is currently a
working assumption in 3GPP Long Term Evolution (LTE) downlink.
Also, OFDMA is the candidate access method for the IEEE 802.22
"Wireless Regional Area Networks".
[0005] NodeB is a term used in UMTS to denote the BTS (base
transceiver station). In contrast with GSM base stations, NodeB
uses WCDMA or OFDMA as air transport technology, depending on the
type of network. As in all cellular systems, such as UMTS and GSM,
NodeB contains radio frequency transmitter(s) and the receiver(s)
used to communicate directly with the mobiles, which move freely
around it. In this type of cellular networks the mobiles cannot
communicate directly with each other but have to communicate with
the BTSs.
[0006] Traditionally, the NodeBs have minimum functionality, and
are controlled by an RNC (Radio Network Controller). However, this
is changing with the emergence of High Speed Downlink Packet Access
(HSDPA), where some logic (e.g. retransmission) is handled on the
NodeB for lower response times and in 3GPP long term evolution
(LTE) wireless networks (a.k.a. E-UTRA--Evolved Universal
Terrestrial Radio Access Network) almost all the RNC
functionalities have moved to the NodeB. A NodeB is generally a
fixed station and may be called a base transceiver system (BTS), an
access point, a base station, or various other names. As the
network has evolved, a NodeB is also referred to as an "evolved
NodeB" (eNB).
[0007] In WCDMA and OFDMA the cell's size is not constant (a
phenomenon known as "cell breathing"). This requires a careful
planning in 3G (UMTS) networks. Power requirements on NodeBs and UE
(user equipment) are typically lower than in GSM.
[0008] A NodeB can serve several cells, also called sectors,
depending on the configuration and type of antenna. Common
configuration include omni cell (360.degree.), 3 sectors
(3.times.120.degree.) or 6 sectors (3 sectors 120.degree. wide
overlapping with 3 sectors of different frequency).
[0009] High-Speed Packet Access (HSPA) is a collection of mobile
telephony protocols that extend and improve the performance of
existing UMTS protocols. Two standards HSDPA and HSUPA have been
established. High Speed Uplink Packet Access (HSUPA) is a
packet-based data service of Universal Mobile Telecommunication
Services (UMTS) with typical data transmission capacity of a few
megabits per second, thus enabling the use of symmetric high-speed
data services, such as video conferencing, between user equipment
and a network infrastructure.
[0010] An uplink data transfer mechanism in the HSUPA is provided
by physical HSUPA channels, such as an Enhanced Dedicated Physical
Data Channel (E-DPDCH), implemented on top of the uplink physical
data channels such as a Dedicated Physical Control Channel (DPCCH)
and a Dedicated Physical Data Channel (DPDCH), thus sharing radio
resources, such as power resources, with the uplink physical data
channels. The sharing of the radio resources results in
inflexibility in radio resource allocation to the physical HSUPA
channels and the physical data channels.
[0011] The signals from different users within the same cell may
interfere with one another. This type of interference is known as
the intra-cell interference. In addition, the base station also
receives the interference from the users transmitting in
neighboring cells. This is known as the inter-cell interference
[0012] When an orthogonal multiple access scheme such as
Single-Carrier Frequency Division Multiple Access (SC-FDMA)--which
includes interleaved and localized Frequency Division Multiple
Access (FDMA) or Orthogonal Frequency Division Multiple Access
(OFDMA)--is used; intra-cell multi-user interference is not
present. This is the case for the next generation of the 3.sup.rd
generation partnership project (3GPP) enhanced-UTRA (E-UTRA)
system--which employs SC-FDMA--as well as IEEE 802.16e also known
as Worldwide Interoperability for Microwave Access (WiMAX)--which
employs OFDMA, In this case, the fluctuation in the total
interference only comes from inter-cell interference and thermal
noise which tends to be slower. While fast power control can be
utilized, it can be argued that its advantage is minimal.
[0013] In the uplink (UL) of OFDMA frequency division multiple
access (both classic OFDMA and SC-FDMA) communication systems, it
is beneficial to provide orthogonal reference signals (RS), also
known as pilot signals, to enable accurate channel estimation and
channel quality indicator (CQI) estimation enabling UL channel
dependent scheduling, and to enable possible additional features
which require channel sounding.
[0014] Channel dependent scheduling is widely known to improve
throughput and spectral efficiency in a network by having the
NodeB, also referred to as base station, assign an appropriate
modulation and coding scheme for communications from and to a user
equipment (UE), also referred to as mobile, depending on channel
conditions such as the received signal-to-interference and noise
ratio (SINR). In addition to channel dependent time domain
scheduling, channel dependent frequency domain scheduling has been
shown to provide substantial gains over purely distributed or
randomly localized (frequency hopped) scheduling in OFDMA-based
systems. To enable channel dependent scheduling, a corresponding
CQI measurement should be provided over the bandwidth of interest.
This CQI measurement may also be used for link adaptation,
interference co-ordination, handover, etc.
[0015] Several control signaling information bits on downlink
transmission need to be transmitted in uplink, as described in 3GPP
TR 25.814 v7.0.0. 3rd Generation Partnership Project; Technical
Specification Group Radio Access Network; Physical layer aspects
for evolved Universal Terrestrial Radio Access (UTRA). For example,
downlink hybrid Automatic Repeat reQuest (ARQ) (HARQ) requires a
1-bit ACK/NACK in uplink for each received downlink transport
block. Further, the downlink channel quality indicator (CQI) needs
to be feedback in the uplink to support frequency selective
scheduling in the downlink. When a UE (user equipment) has uplink
data transmission, the downlink ACK/NACK and/or CQI can be
transmitted along with the uplink data, in which the uplink
reference signal can be used for coherent demodulation of the
uplink data, as well as the downlink ACK/NACK and/or CQI. In case
there is no uplink data transmission, a reference signal can be
transmitted for coherent demodulation of the downlink ACK/NACK
and/or CQI. Thus, multiple dedicated time-frequency resource blocks
are necessary for the reference signal and the ACK/NACK and/or CQI.
While CQI may be transmitted less frequently based on a periodic or
triggered mechanism, ACK/NACK needs to be transmitted in a timely
manner for every received downlink transport block to support HARQ.
Note that ACK/NACK is sometimes denoted as ACKNAK or just simply
ACK, or any other equivalent term.
[0016] User equipments (UE) of an E-UTRAN network are time and
frequency multiplexed on a shared channel (SCH) such that time
(approximately 1 .mu.s) and frequency synchronization are required.
The scheduler, in the base-station, has full control of the time
and frequency locations of uplink transmissions for all connected
user devices, except for UE autonomous transmissions through either
the (non-synchronized) random access channel (RACH) channel or the
scheduling request (SR) channel. To enable proper scheduling and
multi-UE management, each UE should be uniquely identified to a
base-station. The 3GPP working groups have proposed a 16-bit
identifier (ID) for UE's, which represents significant overhead
costs for uplink and downlink control signaling in an E-UTRAN
network because, in practical implementations, at most a few
hundred UE's (compared to 2.sup.16) will be maintained in uplink
synchronization. An uplink synchronized UE can request and have
access to uplink transmissions faster than a non-synchronized UE,
which first needs to recover synchronization.
[0017] In E-UTRA, the non-synchronized physical random access
channel (PRACH) is a contention-based channel multiplexed with
scheduled data in a TDM/FDM manner. It is accessible during PRACH
slots of duration T.sub.RA and period T.sub.RA.
SUMMARY OF THE INVENTION
[0018] An embodiment of the present invention provides a method for
transmitting in a cellular network. User equipment (UE)-initiated
accesses within a cellular network are optimized to account for
cell size and to reduce signaling overhead. A fixed set of preamble
parameter configurations for use across a complete range of cell
sizes within the cellular network is established and stored within
each UE. A UE located in a given cell receives a configuration
number transmitted from a nodeB serving the cell, the configuration
number being indicative of a size of the cell. The UE selects a
preamble parameter configuration from the fixed set of preamble
parameter configurations in response to the received configuration
number and then transmits a preamble from the UE to the nodeB using
the preamble parameter configuration indicated by the configuration
number.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Particular embodiments in accordance with the invention will
now be described, by way of example only, and with reference to the
accompanying drawings:
[0020] FIG. 1 is a pictorial of an illustrative telecommunications
network that supports transmission of multiplexed RA preambles;
[0021] FIG. 2 is an illustrative up-link time/frequency allocation
for use in the network of FIG. 1;
[0022] FIG. 3 illustrates a non-synchronized physical random access
channel (PRACH) preamble structure in time domain for use in the
uplink transmission of FIG. 2;
[0023] FIG. 4 is an illustration of the PRACH preamble structure in
frequency domain for use in the uplink transmission of FIG. 2;
[0024] FIG. 5 is a flow diagram illustrating operation of a
signaling process for selecting a preamble configuration for
transmission of the preamble of FIG. 3;
[0025] FIG. 6 is a block diagram of an illustrative transmitter for
transmitting the preamble structure of FIG. 3;
[0026] FIG. 7A is a block diagram of an illustrative receiver for
receiving the preamble structure of FIG. 3;
[0027] FIG. 7B is a plot of a power delay profile of an example
root sequence received by the receiver of FIG. 7A;
[0028] FIG. 8 is a block diagram illustrating the network system of
FIG. 1; and
[0029] FIG. 9 is a block diagram of a cellular phone for use in the
network of FIG. 1.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0030] Disclosed herein are various systems and methods for
employing a random access channel in a wireless network to
accommodate user equipment operating in cells of varying sizes.
Embodiments of the disclosed invention may be used to access a
wireless network, such as a telecommunications system, employing
random access techniques. A variety of wireless networks employ
random access techniques, for example the Enhanced Universal
Terrestrial Radio Access Network (E-UTRAN), currently being
standardized by the 3GPP working groups. The disclosed embodiments
of the invention are applicable to all such networks. The disclosed
embodiments include apparatus for transmitting random access
signals and a method for transmitting a random access signal
optimized for cellular coverage.
[0031] Embodiments of the present disclosure are directed, in
general, to wireless communication systems, and can be applied to
generate random access transmissions. Random access transmissions
may also be referred to as ranging transmissions, or other
analogous terms.
[0032] User Equipment ("UE") may be either up-link ("UL")
synchronized or UL non-synchronized. That is, UE transmit timing
may or may not be adjusted to align UE transmissions with NodeB
transmission time slots. When the UE UL has not been time
synchronized, or has lost time synchronization, the UE can perform
a non-synchronized random access to request allocation of up-link
resources. Additionally, a UE can perform non-synchronized random
access to register itself at the access point, or for numerous
other reasons. Possible uses of random access transmission are
many, and do not restrict the scope of the present disclosure. For
example, the non-synchronized random access allows the NodeB to
estimate, and if necessary, to adjust the UE's transmission timing,
as well as to allocate resources for the UE's subsequent up-link
transmission. Resource requests from UL non-synchronized UEs may
occur for a variety of reasons, for example: new network access,
data ready to transmit, or handover procedures.
[0033] FIG. 1 shows an illustrative wireless telecommunications
network 100. The illustrative telecommunications network includes
base stations 101, 102, and 103, though in operation, a
telecommunications network may include more base stations or fewer
base stations. Each of base stations 101, 102, and 103 is operable
over corresponding coverage areas 104, 105, and 106. Each base
station's coverage area is further divided into cells. In the
illustrated network, each base station's coverage area is divided
into three cells. Handset or other UE 109 is shown in Cell A 108,
which is within coverage area 104 of base station 101. Base station
101 is transmitting to and receiving transmissions from UE 109. As
UE 109 moves out of Cell A 108, and into Cell B 107, UE 109 may be
"handed over" to base station 102. Assuming that UE 109 is
synchronized with base station 101, UE 109 likely employs
non-synchronized random access to initiate handover to base station
102. The distance over which a random access signal is recognizable
by base station 101 is a factor in determining cell size.
[0034] When UE 109 is not up-link synchronized with base station
101, non-synchronized UE 109 employs non-synchronous random access
(NSRA) to request allocation of up-link 111 time or frequency or
code resources. If UE 109 has data ready for transmission, for
example, traffic data, measurements report, tracking area update,
etc., UE 109 can transmit a random access signal on up-link 111 to
base station 101. The random access signal notifies base station
101 that UE 109 requires up-link resources to transmit the UE's
data. Base station 101 responds by transmitting to UE 109, via
down-link 110, a message containing the parameters of the resources
allocated for UE 109 up-link transmission along with a possible
timing error correction. After receiving the resource allocation
and a possible timing adjustment message transmitted on down-link
110 by base station 101, UE 109 may adjust its transmit timing, to
bring the UE 109 into synchronization with base station 101, and
transmit the data on up-link 111 employing the allotted resources
during the prescribed time interval.
[0035] FIG. 2 illustrates an exemplary up-link transmission frame
202, and the allocation of the frame to scheduled and random access
channels. The illustrative up-link transmission frame 202,
comprises a plurality of transmission sub-frames. Sub-frames 203
are reserved for scheduled UE up-link transmissions. Interspersed
among scheduled sub-frames 203, are time and frequency resources
allocated to random access channels 201, 210. In the illustration
of FIG. 2, a single sub-frame supports two random access channels.
Note that the illustrated number and spacing of random access
channels is purely a matter of convenience; a particular
transmission frame implementation may allocate more or less
resource to random access channels. Including multiple random
access channels allows more UEs to simultaneously transmit a random
access signal without collision. However, because each UE
independently chooses the random access channel on which it
transmits, collisions between UE random access signals may
occur.
[0036] FIG. 3 illustrates an embodiment of a random access signal
300. The illustrated embodiment comprises cyclic prefix 302, random
access preamble 304, and guard interval 306. Random access signal
300 is one transmission time interval 308 in duration. Transmission
time interval 308 may comprise one or more sub-frame 203 durations.
Note that the time allowed for random access signal transmission
may vary, and this variable transmission time may be referred to as
transmitting over a varying number of transmission time intervals,
or as transmitting during a transmission time interval that varies
in duration. This disclosure applies the term "transmission time
interval" to refer to the time allocated for random access signal
transmission of any selected duration, and it is understood that
this use of the term is equivalent to uses referring to
transmission over multiple transmission time intervals. The time
period allotted for random access signal transmission may also be
referred to as a random access time slot.
[0037] Cyclic prefix 302 and guard interval 306 are typically of
unequal duration. Guard interval 306 has duration equal to
approximately the maximum round trip delay of the cell while cyclic
prefix 302 has duration equal to approximately the sum of the
maximum round trip delay of the cell and the maximum delay spread.
As indicated, cyclic prefix and guard interval durations may vary
from the ideal values of maximum round trip delay and maximum delay
spread while effectively optimizing the random access signal to
maximize coverage. All such equivalents are intended to be within
the scope of the present disclosure.
[0038] Round trip delay is a function of cell size, where cell size
is defined as the maximum distance d at which a UE can interact
with the cell's base station. Round trip delay can be approximated
using the formula t=d*20/3 where t and d are expressed in
microseconds and kilometers respectively. The round-trip delay is
the two-way radio propagation delay in free space, which can be
approximated by the delay of the earlier radio path. A typical
earlier path is the line-of-sight path, defined as the direct
(straight-line) radio path between the UE and the base station.
When the UE is surrounded by reflectors, its radiated emission is
reflected by these obstacles, creating multiple, longer traveling
radio paths. Consequently, multiple time-delayed copies of the UE
transmission arrive at the base station. The time period over which
these copies are delayed is referred to as "delay spread," and for
example, in some cases, 5 .mu.s may be considered a conservative
value thereof.
[0039] Cyclic prefix 302 serves to absorb multi-path signal energy
resulting from reflections of a signal transmitted in the prior
sub-frame, and to simplify and optimize equalization at the NodeB
101 receiver by reducing the effect of the channel transfer
function from a linear (or aperiodic) correlation to a cyclic (or
periodic) correlation operated across the observation interval 310.
Guard interval 306 follows random access preamble 304 to prevent
interference between random access preamble signal 304 and any
transmission in the subsequent sub-frame on the same transmission
frequencies used by random access preamble signal 304.
[0040] Random access preamble signal 304 is designed to maximize
the probability of preamble detection by the NodeB and to minimize
the probability of false preamble detections by the NodeB, while
maximizing the total number of resource opportunities. Embodiments
of the present disclosure utilize constant amplitude zero
autocorrelation ("CAZAC") sequences to generate the random access
preamble signal. CAZAC sequences are complex-valued sequences with
the following two properties: 1) constant amplitude (CA), and 2)
zero cyclic autocorrelation (ZAC).
[0041] The preamble sequence is a long CAZAC complex sequence
allocated to the UE among a set of R.sub.S possible sequences.
These sequences are built from cyclic shifts of a CAZAC root
sequence. If additional sequences are needed, they are built from
cyclic shifts of other CAZAC root sequences.
[0042] Well known examples of CAZAC sequences include, but are not
limited to: Chu Sequences, Frank-Zadoff Sequences, Zadoff-Chu (ZC)
Sequences, and Generalized Chirp-Like (GCL) Sequences. A known set
of sequences with CAZAC property is the Zadoff-Chu N-length
sequences defined as follows
a k = exp [ - j2.pi. M N ( k ( k + 1 ) 2 + qk ) ] ##EQU00001##
where M is relatively prime to N, N odd, and q any integer.
[0043] The latter constraint on N also guarantees the lowest and
constant-magnitude cross-correlation {square root over (N)} between
N-length sequences with different values of M: M.sub.1, M.sub.2
such that (M.sub.1-M.sub.2) is relatively prime to N. As a result,
choosing N a prime number always guarantees this property for all
values of M<N, and therefore maximizes the set of additional
sequences, non orthogonal, but with optimal cross-correlation
property. On top of providing additional sequences for a UE to
chose among in a given cell, these sequences are also intended to
be used in neighboring cells, so as to provide good inter-cell
interference mitigation. In this disclosure, the terms: Zadoff-Chu,
ZC, and ZC CAZAC, are used interchangeably. The term CAZAC denotes
any CAZAC sequence, ZC or otherwise.
[0044] In various embodiments of the present disclosure, random
access preamble signal 304 comprises a CAZAC sequence, such as a ZC
sequence. Additional modifications to the selected CAZAC sequence
can be performed using any of the following operations:
multiplication by a complex constant, DFT, IDFT, FFT, IFFT, cyclic
shifting, zero-padding, sequence block-repetition, sequence
truncation, sequence cyclic-extension, and others. Thus, in one
embodiment of the present disclosure, a UE constructs random access
preamble signal 304 by selecting a CAZAC sequence, possibly
applying a combination of the described modifications to the
selected CAZAC sequence, modulating the modified sequence, and
transmitting the resulting random access signal over the air.
[0045] Assuming that a preamble duration allowing reliable
detection at the cell perimeter has been selected, random access
channel coverage is maximized by allocating as much of the
transmission time interval as possible to round trip delay. In a
typical embodiment of the invention, the maximum round trip delay
is taken to be one half of what is left of the transmission time
interval 308 after subtracting the preamble duration 304 and the
maximum delay spread.
Maximum Round Trip Delay=(TTI-Preamble Duration-Delay Spread)/2
[0046] Guard interval 306 is approximately a maximum round trip
delay in duration to allow for mis-timing of the random access
transmission while, in the worst-case of a cell-edge UE, the tail
(or delay spread) of the preamble is absorbed by the cyclic prefix
of the subsequent TTI. The cyclic prefix 302 is set to a duration
of approximately the sum of the maximum round trip delay and the
maximum delay spread. This dimensioning of the cyclic prefix 302
and the guard interval 306 serves to maximize the cell radius over
which the random access channel is effective while maintaining
isolation from adjacent TTIs.
[0047] An alternative embodiment of a random access signal may
assign a duration of maximum round trip delay plus maximum spread
delay to both the cyclic prefix and the guard interval. This
dimensioning needlessly allocates a delay spread duration to the
guard interval that could otherwise be used to increase round trip
delay and thereby increase cell radius.
[0048] Further aspects of embodiments of the Random Access (RA)
channel operation are described in related U.S. patent application
Ser. No. 11/691,549 (atty docket TI-62486) filed 27 Mar. 2007,
entitled "Random Access Structure For Wireless Networks" which is
incorporated herein by reference; and in related U.S. patent
application Ser. No. 11/833,329 (atty docket TI-63609), filed 3
Aug. 2007, entitled "Random Access Structure For Optimal Cell
Coverage" which is incorporated by reference herein.
[0049] Referring again to FIG. 1, UE 109 is traveling in a
direction with a ground speed as indicated by 112. The direction
and ground speed results in a speed component that is relative to
serving NodeB 101. Due to this relative speed of UE moving toward
or away from its serving NodeB a Doppler shift occurs in the
signals being transmitted from the UE to the NodeB resulting in a
frequency shift and/or frequency spread that is speed
dependent.
[0050] The excellent auto/cross-correlation of CAZAC sequences
allows supporting a much larger number of signature opportunities,
64, than the 16 Walsh-Hadamard opportunities offered in the one
version of a UMTS random access channel (RACH) preamble, and this
with very little performance loss, even when two or more preambles
are received in the same Random Access slot. However, the above
performance assumes no or little Doppler spread or frequency shift,
in presence of which, the CS-ZC sequence looses its
zero-auto-correlation property. The latter degradation has been
confirmed by simulations; in one such simulation the result is as
follows: the wrong preamble detection rate when one or more
preambles were sent rises up to 1% and 50% at 120 km/h and 360 km/h
respectively, in the E.sub.P/N.sub.0 region of 18 dB, which is the
RACH target SINR for detection and false alarm (in presence of
noise only) probabilities of 0.99 and 10.sup.-2 respectively.
[0051] The current E-UTRA requirements regarding the performance of
high-speed UE's is specified in as follows: The E-UTRAN shall
support mobility across the cellular network and should be
optimized for low mobile speed from 0 to 15 km/h. Higher mobile
speed between 15 and 120 km/h should be supported with high
performance. Mobility across the cellular network shall be
maintained at speeds from 120 km/h to 350 km/h (or even up to 500
km/h depending on the frequency band) . . . . The mobile speed
above 250 km/h represents special case, such as high-speed train
environment. In such case a special scenario applies for issues
such as mobility solutions and channel models. For the physical
layer parameterization E-UTRAN should be able to maintain the
connection up to 350 km/h, or even up to 500 km/h depending on the
frequency band. Such requirements can be summarized as: the
physical layer should be dimensioned so as to optimize the
performance of low-speed UE's while keeping acceptable performance
for high-speed UE's.
[0052] In order to fulfill the E-UTRAN requirements, the PRACH
preamble sequence length design should address the following
requirements: 1) maximize the number of Zadoff-Chu sequences with
optimal cross-correlation properties; 2) minimize the interference
to/from the surrounding scheduled data on the Physical Uplink
Scheduled Channel (PUSCH).
[0053] The former is guaranteed by choosing a prime-length
sequence. For the latter, since data and preamble OFDM symbols are
neither aligned nor have same durations, strict orthogonality
cannot be achieved. At least, fixing the preamble duration to an
integer multiple of the PUSCH symbol provides some commensurability
between preamble and PUSCH sub-carriers thus providing
orthogonality between some sub-carriers. This also assumes that the
preamble sampling frequency is an integer multiple of the data
symbol sub-carrier spacing. This is achieved with the chosen
allocated bandwidth of seventy-two data symbol sub-carriers for the
PRACH preamble. However, with 800ps duration, the resulting
sequence length is 864, which does not provide the prime number of
requirement one above. Therefore shortening the preamble to a prime
length slightly increases the interference between PUSCH and NSRA
by slightly decreasing the preamble sampling rate
[0054] FIG. 4 is a more detailed illustration of the PRACH preamble
structure for use in the uplink transmission of FIG. 2. Preamble
structure 402 represents the output of the data symbol FFT of the
transmitter illustrating the seventy-two sub-carriers 404 that are
each 15 kHz, while preamble structure 406 represents the output of
the preamble DFT of the transmitter illustrating the 864
sub-carriers 408 that are each 1.25 kHz. This embodiment uses guard
bands 412, 414 to avoid the data interference at preamble edges. A
cautious design of preamble sequence length not only retains a high
inherent processing gain, but also allows a decent avoidance of
strong data interference. In addition, the loss of spectral
efficiency by guard sub-carriers reservation can also be well
controlled at a fine granularity. In this embodiment, each
sub-carrier 408 is 1.25 kHz for 800 .mu.s preamble duration.
[0055] The sequence length 410 of 839 preamble symbol sub-carriers
also is a best trade-off choice since it corresponds to 69.91
symbol sub-carriers in each symbol and offers 72-69.91=2.09 symbol
sub-carriers protection, which is very close to 1 symbol
sub-carrier protection one each side of the preamble. Further
higher/lower prime sequence length adjustments do not provide as
good of integer number sub-carrier protection. More exactly, the
839 preamble sub-carriers 410 are mapped onto the 864 allocated
sub-carriers 408 as follows: twelve and a half zero sub-carriers
412; 839 preamble sub-carriers 410; twelve and a half zero
sub-carriers 414. In another embodiment, guard band 412 may be
thirteen sub-carries while guard band 414 is twelve sub-carriers,
or visa-versa. In yet another embodiment, the guard bands may
comprise other numerical combinations of sub-carriers.
[0056] The time-continuous PRACH preamble signal s(t) is defined
by:
s ( t ) = .beta. PRACH k = 0 N ZC - 1 n = 0 N ZC - 1 x u , v ( n )
- j 2 .pi. nk N ZC j2.pi. ( k + .PHI. + K ( k 0 + 1 / 2 ) ) .DELTA.
f RA ( t - T CP ) ##EQU00002## where ##EQU00002.2## 0 .ltoreq. t
< T SEQ + T CP , ##EQU00002.3##
.beta..sub.PRACH is an amplitude scaling factor and
k.sub.0=k.sub.RAN.sub.SC.sup.RB-N.sub.RB.sup.ULN.sub.SC.sup.RB/2.
T.sub.SEQ is the sequence duration and T.sub.CP is the cyclic
prefix duration. N.sub.sc.sup.RB is the number of data subcarriers
per resource block (RB) and N.sub.RB.sup.UL is the total number of
resource blocks available for UL transmission. The location in the
frequency domain is controlled by the parameter k.sub.RA, expressed
as a resource block number configured by higher layers and
fulfilling
0.ltoreq.k.sub.RA.ltoreq.N.sub.RB.sup.UL-6
The factor
K=.DELTA.f/.DELTA.f.sub.RA
accounts for the difference in subcarrier spacing between the
random access preamble and uplink data transmission. The variable
.phi. defines a fixed offset determining the frequency-domain
location of the random access preamble within the resource blocks.
The PRACH signal takes the following value for .phi.:.phi.=7.
Number of Root Sequences and Cyclic Shift Values
[0057] If a base station can select any number of cyclic shifts
from 0 to 838, then ten or more signaling bits would be required on
the broadcast channel (BCH). It has now been determined that a
fixed set of preamble parameter configurations can be established
for use across a complete range of cell sizes. An approach for
signaling a cyclic shift value N.sub.CS to be used in a cell is to
reduce the full range of possible cyclic shifts to a pre-defined
set of cyclic shift configurations. Sixteen different
configurations allow reducing the cyclic shift signaling to four
bits. The criterion for choosing these cyclic shift values is to
minimize the number of Zadoff-Chu root sequences while maximizing
the associated cell range. In other words, a configuration using r
different root sequences should be fully filled with cyclic shifted
preambles before another root sequence is added. Given that
sixty-four signatures must be generated, a first choice is all
cyclic shift values corresponding to splitting the sequence length
into sub-multiples of 64: N.sub.CS=N/k; k=1, 2, 4, 8, 16, 32, 64.
Table 1 shows the seven resulting N.sub.CS values where all root
sequences generate the same number of cyclic shifted preambles. The
number of root sequences is given for the regular case where no
cyclic shift restrictions apply (low to medium speed cell).
[0058] In the following tables, the cell size is illustrative and
each network operator can have its own way of calculating it, given
a number of guard samples, typical delay spread, etc. The cell size
column gives an example of cell sizes derivations assuming two
guard samples and 5 .mu.s delay spread.
TABLE-US-00001 TABLE 1 Cyclic shift values maximizing the cell size
while minimizing the number of root sequences # of root # of cyclic
sequences shifts per root (no cyclic shift Cyclic shift Cell size
seq. restrictions) (samples) (km) 64 1 13 0.82 32 2 26 2.68 16 4 52
6.40 8 8 104 13.83 4 16 209 28.85 2 32 419 58.89 1 64 0 118.96
[0059] However, the above list is somewhat restrictive in that it
does not provide any intermediate configuration between two and
four root sequences, or between four and eight root sequences.
Therefore, the above rule for maximizing the cell size for a given
number of root sequences is extended to all possible numbers of
root sequences. For a given number of root sequences, the cyclic
shift value is chosen to provide a close to equal number of cyclic
shifts per root sequence, thus maximizing the corresponding cell
size. The next number of root sequences is the minimum number of
root sequences required to carry 64 signatures when the cyclic
shift of the previous configuration is incremented by one sample.
This results in some skipped numbers of root sequences. This
algorithm actually provides fifteen different numbers of root
sequences. In order to make best use of the four bits available to
carry this information, another configuration is added. In this
embodiment, an intermediate configuration in between one and two
root sequences is added. This is to provide a finer granularity at
small cell sizes. Also, it provides an additional configuration for
the two-root sequence case, with an unbalanced number of cyclic
shifted preamble opportunities between the two root sequences, thus
reducing the root sequence collision probability. If such an
unbalanced allocation of cyclic shifted preambles to root sequences
is to be used, it is the most useful for the two-root sequence
case. Thus, the fixed set of preamble parameter configurations
sample the continuous cell size range covered by the network in a
non-linear way, such that a finer configuration granularity is
provided for smaller cells, reflecting the broader deployment of
smaller cells compared to larger cells. Table 2 provides the final
cyclic shift set.
TABLE-US-00002 TABLE 2 PRACH preamble parameters for pre-defined
cell configurations # of root # of cyclic sequences root shifts per
root (no cyclic shift Cyclic shift Configuration # sequences seq.
restrictions) (samples) Cell size (km) 1 All 64 1 13 0.82 2 1 20 2
19 1.68 2 44 3 All 32 2 26 2.68 4 All but last 21 3 38 4.39 Last 22
5 All 16 4 52 6.40 6 All but last 13 5 64 8.11 Last 12 7 All but
last 11 6 76 9.83 Last 9 8 All but last 9 7 83 10.83 Last 10 9 All
8 8 104 13.83 10 1-2 4 10 119 15.98 3-10 7 11 All but last 6 11 139
18.84 Last 4 12 All but last 5 13 167 22.84 Last 4 13 All 4 16 209
28.85 14 All but last 3 22 279 38.86 Last 1 15 All 2 32 419 58.89
16 All 1 64 0 118.96
[0060] Table 3 shows, for the regular case where no cyclic shift
restrictions apply (low to medium speed cell) an alternative
embodiment of a selected set of number of root sequences, chosen to
provide a close to equal number of cyclic shifts per root sequence.
When this is not possible, the rule applied is to have an equal
number of cyclic shifts for all root sequences but the last one,
and to adjust the remaining number of cyclic shifts in the last
root sequence to yield 64 in total. The associated cell size is
provided, for information, and is derived from cyclic shift value
assuming two guard samples and 5 .mu.s maximum delay spread. The
goal is to always try to minimize the number of root sequences for
a given cell range. Since there are eleven different
configurations, the configuration can be signaled on 4 bits.
TABLE-US-00003 TABLE 3 PRACH preamble parameters for pre-defined
cell configurations # of ZC # of cyclic sequences ZC shifts per ZC
(no cyclic shift Cyclic shift Configuration # sequences seq.
restrictions) (samples) Cell size (km) 1 All 64 1 13 0.8 2 All 32 2
26 2.7 3 All but last 21 3 38 4.4 Last 22 4 All 16 4 52 6.4 5 All
but last 13 5 64 8.1 Last 12 6 All but last 11 6 76 9.8 Last 9 7
All 8 8 104 13.8 8 All but last 6 11 139 18.8 Last 4 9 All but last
5 13 167 22.8 Last 4 10 All 4 16 209 28.8 11 All 1 64 839 119.0
[0061] For high speed cells where cyclic shift restrictions apply,
more ZC root sequences will be configured than what is indicated in
the Table 2 and Table 3. The NodeB signals both the cell
configuration number, which identifies the cyclic shift value, and
the additional number of ZC root sequences. Whenever the number of
additional ZC root sequences is greater than zero, the UE infers
that cyclic restrictions apply and identifies which cyclic shifts
must not be used according to operating procedures of the
telecommunications network in which the UE is operating.
[0062] In an alternate embodiment, the NodeB only signals with a
one-bit flag if the current cell is a high speed cell or a normal
cell. In the former case, the UE infers that cyclic restrictions
apply and identifies which cyclic shifts must not be used and
associated additional root sequences according to operating
procedures of the telecommunications network in which the UE is
operating.
[0063] Table 2 and Table 3 provide two representative examples of a
fixed set of preamble parameters. Other embodiments may use
variations of these examples by agreeing upon a different fixed set
of preamble parameters that is stored in each UE used in the
network. In another embodiment, the number of configurations may be
increased to up to thirty-two and therefore five bits be used for
signaling, for example.
[0064] FIG. 5 is a flow diagram illustrating operation of a
signaling process for selecting a preamble configuration for
transmission of the PRACH preamble of FIG. 3 from user equipment to
base stations. The fixed set of preamble parameter configurations
for use across a complete range of cell sizes within the cellular
network is established 502 as discussed above. Once established,
each UE that will operate in the network is preloaded with the
fixed set of preamble configurations. In the present embodiment,
this is done by loading the fixed set of preamble configurations
into a storage circuit, such as a flash read only memory (EPROM) or
other type of random access memory device, in an offline procedure.
In another embodiment, the storage circuit may by loaded or updated
via data downloads from a eNB or other control system within the
network using over the air transmissions. The fixed set of preamble
parameter configurations may be stored on the UE in the form of a
record or table that can be accessed using the configuration number
as an index, for example.
[0065] In addition to the fixed set of parameter configurations
that is preloaded onto all UEs in the cellular network, the
ordering of root sequences and the rule for physical mapping of the
signatures onto the root sequences is preloaded onto all UEs that
will operate within the network.
[0066] As a UE enters a cell, an eNB serving that cell broadcasts
control signaling information to the UE to notify the UE as to what
preamble configuration to use within that cell. The eNB also
broadcasts the index of the first root sequence of the set of
preloaded root sequences and information of whether high speed
cyclic shift restrictions apply within the cell. The UE receives
504 a configuration number from the eNB that is correlated to the
size of the cell, as described in Table 2 for this embodiment. For
example, if the cell size is between 4.26 km and 6.2 km, then the
eNB sends a four-bit configuration number of "0x5" which implicitly
indicates to the UE to form a preamble based on configuration
parameters of sixteen cyclic shifts per root sequence using four
root sequences, as illustrated in Table 2.
[0067] After receiving the configuration number, the UE will store
this value for future reference. When it is time to transmit a
PRACH preamble, the UE selects a preamble parameter configuration
specified by the received configuration number from the fixed set
of preamble parameter configurations. Following the same example,
the UE will select parameter configuration "5" meaning that it will
use the implicit values of four root sequences and sixteen cyclic
shifts per root sequence or in other words each cyclic shift will
shift fifty-two sample positions.
[0068] The UE will then transmit 508 an NSRA preamble to the eNB
using the preamble parameter configuration indicated by the
configuration number.
[0069] Before transmitting the preamble, the UE determines 510 the
cyclic shift value and/or the number of root sequences of the
selected preamble parameter configuration by consulting the stored
fixed set of preamble parameter configurations using the received
configuration number as an index in this embodiment. Other
embodiments may use other schemes to associate the received
configuration number with a corresponding preamble configuration of
the fixed set of preamble parameter configurations that is stored
on the UE.
[0070] In this embodiment there are sixty-four preamble signatures
that may be used by any UE within a given cell. The UE maps 512 the
sixty-four preamble signatures to subsequent cyclic shifts of a
given root sequence according to the number of cyclic shifts until
the given root sequence is full. Generally one root sequence will
not accommodate all sixty-four signatures and mapping continues to
additional root sequences for all of the number of root sequences
until a last root sequence. If the last sequence has a different
number of cyclic shifts as indicated by the selected parameter
configuration, then the UE may adjust 512 the number of cyclic
shifts mapped onto the last root sequence such that the
predetermined number (64) of preamble signatures are mapped.
[0071] After mapping the preamble signatures, the UE selects 514
one of the mapped preamble signatures for use in transmitting 508
the preamble. There are sixty-four total possible signatures. This
set is split as follows: 1) contention-based
signatures/contention-free signatures; 2) the contention-based
signature set is split into two sub-sets: small/large resource
allocation of msg3.
[0072] Contention-free signatures are explicitly allocated to a UE
by the eNB in the case of handover and new downlink data in buffer
for a non-synchronized UE.
[0073] Contention-based signatures are selected by the UE as
follows. First, the UE chooses the relevant subset based on the
size of the UL resource it needs to send as a variable size message
(msg3) on the physical uplink shared channel (PUSCH) after the
preamble. The UE estimates the size of the UL resource based on
msg3 payload and quality of the radio link; the poorer the radio
link quality, the smaller the allocated bandwidth. Then, the UE
picks a signature randomly within the selected signature
subset.
[0074] Regardless of whether the request is contention-based or
contention-free, in this embodiment the transmission will use the
same physical random access channel (PRACH) and preamble structure,
as described herein. Of course, in other embodiments the
contention-free transmissions may be transmitted using a variation
of this scheme or a different scheme.
[0075] FIG. 6 is a block diagram of an illustrative transmitter 600
for transmitting the preamble structure of FIG. 3. Apparatus 600
comprises ZC Root Sequence Selector 601, Cyclic Shift Selector 602,
Repeat Selector 603, ZC Root Sequence Generator 604, Cyclic Shifter
605, DFT in 606, Tone Map 607, other signals or zero-padding in
611, IDFT in 608, Repeater in 609, optional repeated samples 612,
Add CP in 610, and the PRACH signal in 613. Elements of the
apparatus may be implemented as components in a fixed or
programmable processor. In some embodiments, the IDFT block in 608
may be implemented using an Inverse Fast Fourier Transform (IFFT),
and the DFT block in 606 may be implemented using a Fast Fourier
Transform (FFT). Apparatus 600 is used to select and perform the
PRACH preamble signal transmission as follows. The UE performs
selection of the CAZAC (e.g. ZC) root sequence using the ZC Root
Sequence Selector 601 and the selection of the cyclic shift value
using the Cyclic Shift Selector 602. Next, the UE generates the ZC
sequence using the ZC Root Sequence Selector 604. Then, if
necessary, the UE performs cyclic shifting of the selected ZC
sequence using the Cyclic Shifter 605. The UE performs DFT
(Discrete Fourier Transform) of the cyclically shifted ZC sequence
in DFT 606. The result of the DFT operation is mapped onto a
designated set of tones (sub-carriers) using the Tone Map 607.
Additional signals or zero-padding 611, may or may not be present.
The UE next performs IDFT of the mapped signal using the IDFT 608.
The size of the IDFT in 608 may optionally be larger than the size
of DFT in 606.
[0076] In other embodiments, the order of cyclic shifter 605, DFT
606, tone map 607 and IDFT 608 may be arranged in various
combinations. For example, in one embodiment a DFT operation is
performed on a selected root sequence, tone mapping is then
performed, an IDFT is performed on the mapped tones and then the
cyclic shift may be performed. In another embodiment, tone mapping
is performed on the root sequence and then an IDFT is performed on
the mapped tones and then a cyclic shift is performed.
[0077] FIG. 7A is a block diagram of an illustrative receiver for
receiving the preamble structure of FIG. 3. This receiver
advantageously makes use of the time and frequency domain
transforming components used to map and de-map data blocks in the
up-link sub-frame to take full profit of the PRACH format and CAZAC
sequence by computing the PRACH power delay profile through a
frequency-domain computed periodic correlation. Indeed, the power
delay profile pdp(l) of the received sequence is defined as:
pdp yx ( l ) = r yx ( l ) = n = 0 N ZC - 1 y ( n ) x * ( ( n + l )
N ZC ) ( 1 ) ##EQU00003##
where r.sub.yx(l) is the discrete periodic autocorrelation function
at lag l of the received sequence y(n) and the reference searched
CAZAC sequence x(n), and where ( )* and ( ).sub.n denote the
complex conjugate and modulo-n respectively. Given the periodic
convolution of the complex sequences y(n) and x(n) defined as:
[ y ( n ) * x ( n ) ] ( l ) = n = 0 N ZC - 1 y ( n ) x ( ( l - n )
N ZC ) ( 2 ) ##EQU00004##
r.sub.yx(l) can be expressed as follows:
r.sub.xy(l)=(y(n)*x*(-n))(l) (3)
Using the following properties of the Discrete Fourier Transform
(DFT):
Complex sequence DFT
x(n).fwdarw.X(k)
y(n).fwdarw.Y(k)
x*(-n).fwdarw.X*(k)
y(n)*x(n).fwdarw.Y(k)X(k) (4)
r.sub.yx(l) can be computed in frequency domain as:
r.sub.yx=DFT.sup.-1{FT(y(n)) DFT(x(n))*} (5)
[0078] An additional complexity reduction comes from the fact that
different PRACH signatures are generated from cyclic shifts of a
common root sequence. As illustrated in FIG. 7B, the
frequency-domain computation of the power delay profile of a root
sequence provides in one shot the concatenated power delay profiles
of all signatures carried on the same root sequence.
[0079] The received PRACH signal 701, comprising cyclic prefix and
PRACH preamble signal, is input to cyclic prefix removal component
702 which strips the cyclic prefix from the PRACH signal producing
signal 703. Frequency domain transforming component DFT 704 couples
to cyclic prefix removal component 702. Frequency domain
transforming component 704 converts signal 703 into sub-carrier
mapped frequency tones 705. Sub-carrier de-mapping component 706 is
coupled to frequency domain transforming component 704. Sub-carrier
de-mapping component 706 de-maps sub-carrier mapped frequency tones
705 to produce useful frequency tones 707. Product component 711 is
coupled to both sub-carrier de-mapping component 707 and frequency
domain transforming component 709. Frequency domain transforming
component (DFT) 709 converts a preamble root sequence 710, such as
a prime length Zadoff-Chu sequence, into a corresponding set of
pilot frequency tones 708. Complex conjugation of pilot frequency
tones 708 is performed using 721, to produce samples 720. Product
component 711 computes a tone by tone complex multiplication of
received frequency tones 707 with samples 720 to produce a set of
frequency tones 712. Time domain transforming component (IDFT) 713
is coupled to product component 711. Time domain transforming
component 713 converts multiplied frequency tones 712 into
correlated time signal 714. Correlated time signal 714 contains
concatenated power delay profiles of the cyclic shift replicas of
the preamble root sequence 710. Energy detection block 715 is
coupled to time domain transforming block 713. Energy detection
block 715 identifies received preamble sequences by detecting the
time of peak correlation between received schedule request signal
701 and preamble root sequence 710.
[0080] Note that frequency domain transforming component 709 is
called for when using the transmitters illustrated in FIG. 6. When
using an alternative embodiment transmitter that does not perform a
DFT, frequency domain transforming component 709 may be
omitted.
[0081] FIG. 8 is a block diagram illustrating the network system of
FIG. 1. As shown in FIG. 8, the wireless networking system 115
comprises a user device 132 in communication with a base-station
150. The user device 132 may represent any of a variety of devices
such as a server, a desktop computer, a laptop computer, a cellular
phone, a Personal Digital Assistant (PDA), a smart phone or other
electronic devices. In some embodiments, the electronic device 132
communicates with the base-station 150 based on a LTE or E-UTRAN
protocol. Alternatively, another communication protocol now known
or later developed is used.
[0082] As shown, the electronic device 132 comprises a processor
138 coupled to a memory 134 and a transceiver 140. The memory 134
stores applications 136 for execution by the processor 138. The
applications 136 could comprise any known or future application
useful for individuals or organizations. As an example, such
applications 136 could be categorized as operating systems, device
drivers, databases, multimedia tools, presentation tools, Internet
browsers, emailers, Voice Over Internet Protocol (VOIP) tools, file
browsers, firewalls, instant messaging, finance tools, games, word
processors or other categories. Regardless of the exact nature of
the applications 136, at least some of the applications 136 may
direct the user device 132 to transmit uplink signals to the
base-station 150 periodically or continuously via the transceiver
140. Over time, different uplink transmissions from the user device
132 may be high priority (time-critical) or low priority (non-time
critical). In at least some embodiments, the user device 132
identifies a Quality of Service (QoS) requirement when requesting
an uplink resource from the base-station 150. In some cases, the
QoS requirement may be implicitly derived by the base-station 150
from the type of traffic supported by the user device 132. As an
example, VOIP and gaming applications often involve high priority
uplink transmissions while High Throughput (HTP)/Hypertext
Transmission Protocol (HTTP) traffic involves low priority uplink
transmissions.
[0083] As shown in FIG. 8, the transceiver 140 comprises uplink
logic 120, which enables the user device 132 to request an uplink
resource from the base-station 150 and upon a successful request to
send uplink transmissions to the base-station 150. In FIG. 8, the
uplink logic 120 comprises resource request logic 122, synchronize
logic 124, and time-out logic 126. As would be understood by one of
skill in the art, the components of the uplink logic 120 may
involve the physical (PHY) layer and/or the Media Access Control
(MAC) layer of the transceiver 140.
[0084] In at least some embodiments, the resource request logic 122
detects when the user device 132, in absence of any valid uplink
resource grant, needs to send an uplink transmission to the
base-station 150 and submits a corresponding scheduling request. If
the user device 132 is not uplink synchronized, the scheduling
request is made using the non-synchronized physical random access
channel (PRACH) 186, which is potentially contentious depending on
how many other user devices also need to use the PRACH at the same
time (e.g., for scheduling requests or uplink synchronization
maintenance). Alternatively, if the user device 132 is uplink
synchronized, the resource request may be submitted via a
contention-free scheduling request channel 192 which may be
available to the user device 132. In either case, the request is
made using preamble structure 300, depending on the relative speed
of the UE to the NodeB and how a particular cell is configured, as
described earlier. A command received from the base station
indicates what preamble configuration is to be used in a given
cell, as described in more detail above.
[0085] In at least some embodiments, the scheduling request channel
192 is part of the dedicated channels 184. The dedicated channels
184 represent uplink synchronized channels which are dedicated to a
particular purpose and which are selectively accessible to one or
more user devices. Another example of dedicated channel is the
sounding reference signal (SRS). The SRS is a standalone reference
signal (or pilot) which provides means to the base-station to
perform channel quality information (CQI) estimation for frequency
dependent scheduling, to maintain uplink synchronization, and to
implement link adaptation and power control for each user.
[0086] If the user device 132 previously obtained a resource
allocation from the base station 150 and the resource allocation
has not expired, uplink transmissions can be sent via a shared
channel 182 (i.e., a channel shared with other user devices based
on time and division multiplexing) in the form of a MAC Packet Data
Unit (PDU) transmission. In at least some embodiments, the resource
request logic 122 also detects when the user device 132, with at
least one valid uplink resource grant, needs to update its current
allocated uplink resource(s) (e.g., if the user device 132 needs
more resources because it received more data in its transmission
buffer) and submits a corresponding scheduling request. Since the
user device 132 already has valid uplink grants, it is uplink
synchronized, and the resource request may be either embedded in a
MAC PDU sent on these valid grants on the uplink shared channel
182, or submitted via the scheduling request channel 192.
[0087] To use the shared channel 182 or the scheduling request
channel 192, the user device 132 receives a unique identifier from
the base-station 150. In some embodiments, the unique identifier is
explicitly provided by the base-station 150 (e.g., the base-station
150 broadcasts a multi-bit unique identifier to the user device 132
for use with the shared channel 182). In alternative embodiments,
the unique identifier is implicitly provided by the base-station
150 (e.g., the base-station 150 provides a one- to-one mapping
between the user device 132 and a physical uplink resource of the
scheduling request channel 192).
[0088] The synchronize logic 124 enables the user device 132 to
maintain a particular synchronization for uplink transmissions via
the shared channel 182 or other uplink synchronized channels (e.g.,
the SRS or the scheduling request channel 192). In some
embodiments, the synchronize logic 124 supports time and frequency
adjustments based on a predetermined protocol and/or instructions
from the base-station 150. Once the user device 132 is
synchronized, the synchronization can be periodically updated based
on timers and/or information exchanged between the user device 132
and the base-station 150. For example, if the user device 132 is
synchronized and has at least one scheduling grant from the
base-station 150, then the synchronize manager 174 of the
base-station 150 can maintain the user device's synchronization
based on ongoing uplink transmissions from the user device 132 via
the shared channel 182.
[0089] If the user device 132 is synchronized but does not have a
scheduling grant from the base-station 150, then the synchronize
manager 174 of the base-station 150 can maintain the user's
synchronization based on a PRACH transmission 186. Alternatively,
if the user device 132 is synchronized but does not have a
scheduling grant from the base-station 150, then the synchronize
manager 174 of the base-station 150 can maintain the user's
synchronization based on information transmitted via one of the
dedicated channels 184 (e.g., using a SRS or an autonomous
synchronization request from the user device 132 through the
scheduling request channel 192). By appropriately synchronizing
uplink transmissions of the user device 132, interference to and
from the transmissions of other user devices can be avoided and
orthogonal multiplexing is maintained.
[0090] As shown in FIG. 8, the base-station 150 comprises a
processor 154 coupled to a memory 156 and a transceiver 170. The
memory 156 stores applications 158 for execution by the processor
154. The applications 158 could comprise any known or future
application useful for managing wireless communications. At least
some of the applications 158 may direct the base-station to manage
transmissions to or from the user device 132.
[0091] As shown in FIG. 8, the transceiver 160 comprises an uplink
resource manager 170, which enables the base-station 150 to
selectively allocate uplink resources to the user device 132. In
FIG. 8, the uplink resource manager 170 comprises a state manager
172, a synchronize manager 174, a scheduling grants manager 176 and
a time-out manager 178. As would be understood by one of skill in
the art, the components of the uplink resource manager 170 may
involve the physical (PHY) layer and/or the Media Access Control
(MAC) layer of the transceiver 160.
[0092] Transceiver 160 includes a receiver as described in more
detail in FIG. 7. As discussed previously, a management application
on the NodeB determines what preamble configuration of a fixed set
of preamble parameter configurations will be used in a particular
cell, based on cell sized. The NodeB broadcasts this information to
all UE in the cell as part of system and cell-specific information
on a broadcast channel (BCH).
[0093] In at least some embodiments, the state manager 172
determines whether to assign the user device 132 to a synchronized
state or to a non-synchronized state. In at least some embodiments,
the user device 132 can request to be assigned to the synchronized
state using PRACH 186.
[0094] If the user device 132 is accepted into the synchronized
state, a reduced identifier is provided to the user device 132. The
reduced identifier enables the user device 132 to send uplink
transmissions via the shared channel 182 and new resource requests
via the scheduling requests channel 192. In some embodiments, the
state manager 172 enables the reduced identifier to be explicitly
provided to the user device 132 (e.g., broadcasting a multi-bit
unique identifier to the user device 132 for use with the shared
channel 182). In alternative embodiments, the state manager 172
enables the unique identifier to be implicitly provided to the user
device 132 (e.g., providing a one-to-one mapping between the user
device 132 and a physical uplink resource of the base-station 150).
If the user device 132 becomes non-synchronized due to a time-out
or any other reason, the state manager 172 reassigns the user
device 132 to the non-synchronized state and releases the reduced
identifier and any associated uplink resource that was assigned to
the user device 132.
[0095] The synchronize manager 174 maintains user devices in
synchronization for uplink transmissions via the shared channel 182
or any dedicated channel 184. In order to do so, the synchronize
manager 174 estimates the timing error of the uplink transmissions
of the user device 132 on either the shared channel 182, a
dedicated channel 184 (e.g., SRS) or the PRACH 186. Then, the
synchronize manager 174 sends back a timing advance (TA) command to
the user device 132, that will be executed by the synchronize logic
124. By appropriately synchronizing uplink transmissions of the
user device 132, the synchronize manager 174 avoids interferences
between uplink transmissions of the user device 132 and uplink
transmissions of other user devices and orthogonal multiplexing is
maintained.
[0096] The scheduling grants manager 176 selectively determines
when synchronized user devices will be scheduled on the shared
channel 182. For example, the scheduling grants manager 176 may
assign scheduling grants in response to new resource requests from
user device 132 sent through the scheduling request channel
192.
[0097] If more than a threshold amount of time passes during which
the user device 132 does not send any uplink transmissions, a
time-out may occur. The time-out manager 178 determines when a
time-out occurs based on one or more time-out thresholds 190. In at
least some embodiments, the time-out manager 178 implements timers
or counters to track the amount of time that passes between uplink
transmissions for all synchronized user devices. The time-out
thresholds 190 may be predetermined or may be determined, for
example, based on the number of user devices in communication with
the base-station.
[0098] In at least some embodiments, a time-out threshold causes
user devices to enter the non-synchronized state. Typically, the
entrance of user devices to the non-synchronized state does not
depend on exchanging messages between the base station 150 and user
devices. In other words, both user devices and the base-station 150
can track the passage of time separately and independently
determine that a user device is in a non-synchronized state. In
case a user device transitions to the non-synchronized state, any
existing uplink grant of this user device is released.
[0099] FIG. 9 is a block diagram of a UE 1000 that stores a fixed
set of preamble parameter configurations for use across a complete
range of cell sizes within the cellular network, as described
above. Digital system 1000 is a representative cell phone that is
used by a mobile user. Digital baseband (DBB) unit 1002 is a
digital processing processor system that includes embedded memory
and security features.
[0100] Analog baseband (ABB) unit 1004 performs processing on audio
data received from stereo audio codec (coder/decoder) 1009. Audio
codec 1009 receives an audio stream from FM Radio tuner 1008 and
sends an audio stream to stereo headset 1016 and/or stereo speakers
1018. In other embodiments, there may be other sources of an audio
stream, such a compact disc (CD) player, a solid state memory
module, etc. ABB 1004 receives a voice data stream from handset
microphone 1013a and sends a voice data stream to handset mono
speaker 1013b. ABB 1004 also receives a voice data stream from
microphone 1014a and sends a voice data stream to mono headset
1014b. Usually, ABB and DBB are separate ICs. In most embodiments,
ABB does not embed a programmable processor core, but performs
processing based on configuration of audio paths, filters, gains,
etc being setup by software running on the DBB. In an alternate
embodiment, ABB processing is performed on the same processor that
performs DBB processing. In another embodiment, a separate DSP or
other type of processor performs ABB processing.
[0101] RF transceiver 1006 includes a receiver for receiving a
stream of coded data frames and commands from a cellular base
station via antenna 1007 and a transmitter for transmitting a
stream of coded data frames to the cellular base station via
antenna 1007. A command received from the base station indicates
what configuration number of the fixed set of preamble parameter
configurations is to be used in a given cell, as described in more
detail above.
[0102] A non-synchronous PRACH signal is transmitted using a
selected preamble structure based on cell size when data is ready
for transmission as described above; in response, scheduling
commands are received from the serving base station. Among the
scheduling commands can be a command (implicit or explicit) to use
a particular sub-channel for transmission that has been selected by
the serving NodeB. Transmission of the scheduled resource blocks
are performed by the transceiver using the sub-channel designated
by the serving NodeB. Frequency hopping may be implied by using two
or more sub-channels as commanded by the serving NodeB. In this
embodiment, a single transceiver supports OFDMA and SC-FDMA
operation but other embodiments may use multiple transceivers for
different transmission standards. Other embodiments may have
transceivers for a later developed transmission standard with
appropriate configuration. RF transceiver 1006 is connected to DBB
1002 which provides processing of the frames of encoded data being
received and transmitted by cell phone 1000.
[0103] The basic SC-FDMA DSP radio can include DFT, subcarrier
mapping, and IFFT (fast implementation of IDFT) to form a data
stream for transmission and DFT, subcarrier de-mapping and IFFT to
recover a data stream from a received signal, as described in more
detail in FIGS. 6-7. DFT, IFFT and subcarrier mapping/de-mapping
may be performed by instructions stored in memory 1012 and executed
by DBB 1002 in response to signals received by transceiver
1006.
[0104] DBB unit 1002 may send or receive data to various devices
connected to USB (universal serial bus) port 1026. DBB 1002 is
connected to SIM (subscriber identity module) card 1010 and stores
and retrieves information used for making calls via the cellular
system. DBB 1002 is also connected to memory 1012 that augments the
onboard memory and is used for various processing needs. DBB 1002
is connected to Bluetooth baseband unit 1030 for wireless
connection to a microphone 1032a and headset 1032b for sending and
receiving voice data.
[0105] DBB 1002 is also connected to display 1020 and sends
information to it for interaction with a user of cell phone 1000
during a call process. Display 1020 may also display pictures
received from the cellular network, from a local camera 1026, or
from other sources such as USB 1026.
[0106] DBB 1002 may also send a video stream to display 1020 that
is received from various sources such as the cellular network via
RF transceiver 1006 or camera 1026. DBB 1002 may also send a video
stream to an external video display unit via encoder 1022 over
composite output terminal 1024. Encoder 1022 provides encoding
according to PAL/SECAM/NTSC video standards.
[0107] As used herein, the terms "applied," "coupled," "connected,"
and "connection" mean electrically connected, including where
additional elements may be in the electrical connection path.
"Associated" means a controlling relationship, such as a memory
resource that is controlled by an associated port. The terms
assert, assertion, de-assert, de-assertion, negate and negation are
used to avoid confusion when dealing with a mixture of active high
and active low signals. Assert and assertion are used to indicate
that a signal is rendered active, or logically true. De-assert,
de-assertion, negate, and negation are used to indicate that a
signal is rendered inactive, or logically false.
[0108] While the invention has been described with reference to
illustrative embodiments, this description is not intended to be
construed in a limiting sense. Various other embodiments of the
invention will be apparent to persons skilled in the art upon
reference to this description.
[0109] Embodiments of this invention apply to any flavor of
frequency division multiplex based transmission. Thus, the concept
of valid specification of sub-channels can easily be applied to:
OFDMA, OFDM, DFT-spread OFDM, DFT-spread OFDMA, SC-OFDM, SC-OFDMA,
MC-CDMA, and all other FDM-based transmission strategies.
[0110] A NodeB is generally a fixed station and may also be called
a base transceiver system (BTS), an access point, or some other
terminology. A UE, also commonly referred to as terminal or mobile
station, may be fixed or mobile and may be a wireless device, a
cellular phone, a personal digital assistant (PDA), a wireless
modem card, and so on.
[0111] In a general embodiment of the present disclosure, the set
of allowed PRACH preamble signals is defined by two other sets: 1)
a set of allowed root CAZAC sequences, and 2) a set of allowed
modifications to a given root CAZAC sequence. In one embodiment,
PRACH preamble signal is constructed from a CAZAC sequence, such as
a ZC sequence. Additional modifications to the selected CAZAC
sequence can be performed using any of the following operations:
multiplication by a complex constant, DFT, IDFT, FFT, IFFT, cyclic
shifting, zero-padding, sequence block-repetition, sequence
truncation, sequence cyclic-extension, and others. Thus, in various
embodiments of the present disclosure, a UE constructs a PRACH
preamble signal by selecting a CAZAC sequence, possibly applying a
combination of the described modifications to the selected CAZAC
sequence, modulating the modified sequence, and transmitting the
resulting PRACH signal over the air.
[0112] In some embodiments, the fixed set of preamble parameters
stores both the cyclic shift values and the number of root
sequences, while in other embodiments the cyclic shift values are
stored and the number of root sequences is computed from the cyclic
shift values.
[0113] It is therefore contemplated that the appended claims will
cover any such modifications of the embodiments as fall within the
true scope and spirit of the invention.
* * * * *